1. Field of the Invention
The present invention relates to a method for manufacturing a flash memory cell, and more specifically, to a method for manufacturing a flash memory cell which can prevent a smiling phenomenon of an ONO dielectric film due to a re-oxidization process.
2. Discussion of Related Art
Recently, in flash devices, a program state or erase state is displayed through storage and discharging of electric charges. In such a program and erase, in case of NAND flash devices, program and erase operations are performed through FN tunneling using a high voltage of over 15V and several transistors are operated within a selected cell at the same time. Moreover, within the selected cell, only when charges as many as the number predetermined upon application of a predetermined voltage are stored, it is recognized as a cell of a program state in the flash device.
As the design rule shrinks, however, the effective channel length that may generate FN tunneling is reduced. An oxidization process is usually performed in a subsequent thermal process that has to be necessarily carried out in order to release plasma damage caused upon etching for gate formation. Further, a thickness is increased because of abnormal oxidization that occurs at the side of an ONO dielectric film by means of such a re-oxidation process, thereby causing a so-called smiling phenomenon. As a result, there is a problem that reliability of the device is degraded such as a reduced program speed because a voltage applied to the gate is transferred irregularly.